Is there a way to make Spring Thymeleaf process a string template? - spring-mvc

Question

I would like to write something like :
#Autowired
private SpringTemplateEngine engine;
....
// Thymeleaf Context
WebContext thymeleafContext = new WebContext(request, response, request.getServletContext(), locale);
// cached html of a thymeleaf template file
String cachedHtml=....
// process the cached html
String html=engine.process(cachedHtml, thymeleafContext);
By default, the [process] method can't do that. I can understand from the docs that I need a special Template Resolver :
In order to execute templates, the process(String, IContext) method will be used:
final String result = templateEngine.process("mytemplate", ctx);
The "mytemplate" String argument is the template name, and it will relate to the physical/logical location of the template itself in a way configured at the template resolver/s.
Does anyone know how to solve my problem ?
The goal is to cache the Thymeleaf templates (files) in strings and then process theses strings rather than the files.

Answer 1

The solution we ended up using consisted of a new IResourceResolver with a custom Context rather than a custom TemplateResolver. We chose this because we still wanted to use classpath scanning in most cases, but occasionally had dynamic content.
The following shows how we did it:
public class StringAndClassLoaderResourceResolver implements IResourceResolver {
public StringAndClassLoaderResourceResolver() {
super();
}
public String getName() {
return getClass().getName().toUpperCase();
}
public InputStream getResourceAsStream(final TemplateProcessingParameters params, final String resourceName) {
Validate.notNull(resourceName, "Resource name cannot be null");
if( StringContext.class.isAssignableFrom( params.getContext().getClass() ) ){
String content = ((StringContext)params.getContext()).getContent();
return IOUtils.toInputStream(content);
}
return ClassLoaderUtils.getClassLoader(ClassLoaderResourceResolver.class).getResourceAsStream(resourceName);
}
public static class StringContext extends Context{
private final String content;
public StringContext(String content) {
this.content = content;
}
public StringContext(String content, Locale locale) {
super(locale);
this.content = content;
}
public StringContext(String content, Locale locale, Map<String, ?> variables) {
super(locale, variables);
this.content = content;
}
public String getContent() {
return content;
}
}
Test Case
public class StringAndClassLoaderResourceResolverTest {
private static SpringTemplateEngine templateEngine;
#BeforeClass
public static void setup(){
TemplateResolver resolver = new TemplateResolver();
resolver.setResourceResolver(new StringAndClassLoaderResourceResolver());
resolver.setPrefix("mail/"); // src/test/resources/mail
resolver.setSuffix(".html");
resolver.setTemplateMode("LEGACYHTML5");
resolver.setCharacterEncoding(CharEncoding.UTF_8);
resolver.setOrder(1);
templateEngine = new SpringTemplateEngine();
templateEngine.setTemplateResolver(resolver);
}
#Test
public void testStringResolution() {
String expected = "<div>dave</div>";
String input = "<div th:text=\"${userName}\">Some Username Here!</div>";
IContext context = new StringAndClassLoaderResourceResolver.StringContext(input);
context.getVariables().put("userName", "dave");
String actual = templateEngine.process("redundant", context);
assertEquals(expected, actual);
}
#Test
public void testClasspathResolution(){
IContext context = new Context();
context.getVariables().put("message", "Hello Thymeleaf!");
String actual = templateEngine.process("dummy", context);
String expected = "<h1>Hello Thymeleaf!</h1>";
assertEquals(expected, actual);
}
}
Dummy template file at src/main/resources/mail/dummy.html
<h1 th:text="${message}">A message will go here!</h1>
Note: We used Apache CommonsIO's IOUtils for converting the String to an InputStream

Answer 2

You can implement your own TemplateResolver and IResourceResolver to work with String.

Answer 3

for simple unit tests:
static class TestResourceResolver implements IResourceResolver {
public String content = "";
#Override
public String getName() {
return "TestTemplateResolver";
}
#Override
public InputStream getResourceAsStream(TemplateProcessingParameters templateProcessingParameters,
String resourceName) {
return new ByteArrayInputStream(content.getBytes());
}
}
or just use org.thymeleaf.templateresolver.StringTemplateResolver in Thymeleaf 3

Answer 4

Yep StringTemplateResolver is the way to go.
public class ReportTemplateEngine {
private static TemplateEngine instance;
private ReportTemplateEngine() {}
public static TemplateEngine getInstance() {
if(instance == null){
synchronized (ReportTemplateEngine.class) {
if(instance == null) {
instance = new TemplateEngine();
StringTemplateResolver templateResolver = new StringTemplateResolver();
templateResolver.setTemplateMode(TemplateMode.HTML);
instance.setTemplateResolver(templateResolver);
}
}
}
return instance;
}
}